Method of manufacturing semiconductor device

ABSTRACT

Precisely forming a fine resist pattern on a stopper film of silicon nitride, in a method of manufacturing a multi-layer interconnection structure which uses the stopper film. A silicon nitride film forming step is a step to select a thickness of a silicon nitride film to thereby reduce reflection light of an excimer laser which impinges upon a photoresist layer on the silicon nitride film from the back surface of the photoresist layer.

BACKGROUND OF THE INVENTION

The present invention relates to a method of manufacturing asemiconductor device with a multi-layer interconnection structure.

FIG. 3 shows a conventional method of manufacturing a semiconductordevice with multi-layer interconnection structure described in JP,7-240466, A. In this method, first, as shown in FIG. 3A, a lower wiringlayer 12 is formed on a semiconductor substrate 11. Following this, aninter-layer insulation layer 13 of SiO2 or the like and a stopper film14 of SiN are successively stacked. The inter-layer insulation layer 13and the stopper film 14 are thereafter etched using a resist mask (notshown), thereby forming an aperture portion 15. A plug layer 16 oftungsten or the like is formed so as to fill up the aperture portion 15.

Following this, as shown in FIG. 3B, the plug layer 16 is etched backusing the stopper film 14 as an etching stopper. The plug layer 16 isover-etched so as to completely remove the plug layer 16 on the stopperfilm 14. Therefore, the top surface of the plug layer 16 becomesslightly lower than the surface of the stopper film.

Next, as shown in FIG. 3C, the stopper film 14 is removed usingphosphoric acid. In consequence, the top surface of the plug layer 16projects above the surface of the inter-layer insulation layer 13.

At last, as shown in FIG. 3D, an upper wiring layer 17 is formed. Thesteps described above complete a semiconductor device with a multi-layerinterconnection structure 200 in which the plug layer 16 connects thelower wiring layer 12 with the upper wiring layer 17.

During these steps, since the top surface of the plug layer 16 projectsabove the surface of the inter-layer insulation layer 13 as shown inFIG. 3C, the connection between the plug layer 16 and the upper wiringlayer 17 becomes perfect.

However, as an aperture size of the aperture portions 15 becomes smallin semiconductor devices because of increasing progress of integration,the size and shape of the aperture portions 15 become various.Consequently the connection, etc., between the plug layer 16 and theupper wiring layer 17 becomes imperfect.

Research on a cause of this identified that during exposure of a resistlayer (not shown) formed on the stopper film 14, exposure lightreflected by the surfaces of the stopper film 14 and the inter-layerinsulation layer 13 once again impinges upon and sensitizes the resistlayer, and therefore, it is impossible to precisely form a fine resistpattern. The reflection of the exposure light, in particular, was foundto be remarkable in the case of exposure light with a short wavelengthsuch as an excimer laser.

SUMMARY OF THE INVENTION

Noting this, the present invention aims at providing a method tomanufacture a multi-layer interconnection structure which uses a stopperfilm, with which it is possible to precisely form a fine resist patternon the stopper film.

The present invention is directed to a manufacturing method for asemiconductor device with a multi-layer interconnection structure,comprising: a step to prepare a semiconductor substrate; a step to forman inter-layer insulation layer on said semiconductor substrate; asilicon nitride film forming step to form a silicon nitride film on saidinter-layer insulation layer; a step to form a photoresist layer on saidsilicon nitride film and exposing said photoresist with an excimer laserto thereby form a resist mask; an etching step to etch at least saidsilicon nitride film using said resist mask as an etching mask tothereby form an aperture portion; a step to deposit a conductive layerwithin said aperture portion and on said silicon nitride film; a step toetch back said conductive layer on said silicon nitride film using saidsilicon nitride film as a stopper so that the conductive layer remainingwithin said aperture portion becomes a plug layer; a step to remove thesilicon nitride film so that a top end of the plug layer protrudes abovethe surface of the inter-layer insulation layer; and a step to form awiring layer connected with said plug layer on said inter-layerinsulation layer, wherein said silicon nitride film forming step is astep to select the film thickness of said silicon nitride film in such amanner that reflection light of said excimer laser which impinges uponsaid photoresist layer from the back surface of the photoresist layerdecreases.

With the reflection light decreased in this manner, it is possible toaccurately and precisely form a resist mask with a fine opening pattern.As a result, it is possible to form highly-integrated multi-layerinterconnection structures with an excellent reproducibility and at ahigh yield.

The silicon nitride film forming step described above is preferably astep to select the film thickness of said silicon nitride film in such amanner that a reflectance ratio of the reflection light of the excimerlaser relative to incident light is 0.3 or lower.

Since the reflectance ratio is 0.3 or lower, it is possible to preciselyform a finer resist pattern.

The silicon nitride film forming step described above is preferably astep to select the film thickness of said silicon nitride film from therange of about 1200 Å to about 1340 Å and the range of about 1730 Å toabout 1880 Å.

As the silicon nitride film has such a film thickness, it is possible toensure that the reflectance ratio of the excimer laser is 0.3 orsmaller.

The silicon nitride film forming step described above is preferably astep to select the film thickness of the silicon nitride film from therange of about 1230 Å to about 1310 Å and the range of about 1760 Å toabout 1850 Å.

As the silicon nitride film has such a thickness, it is possible toensure that the reflectance ratio of the excimer laser is 0.2 or lower.

The silicon nitride film forming step is preferably a step to selecteither about 1270 Å or about 1800 Å for the film thickness of saidsilicon nitride film.

As the silicon nitride film has such a film thickness, it is possible tominimize the reflectance ratio of the excimer laser.

A wavelength of the excimer layer described above is about 248 nm. Thethickness of the silicon nitride film described above is effective inreducing the reflectance ratio of the excimer laser with thiswavelength.

The etching step described above preferably comprises a step to etch thesilicon nitride film using the resist mask described above, and afterremoving said resist mask, further to etch the inter-layer insulationlayer mentioned above using said silicon nitride film as a mask.

Etching the inter-layer insulation layer using the silicon nitride filmas a mask, it is possible to prevent the mask from receding during theetching, and hence, to precisely form an aperture portion with a highaspect ratio.

A step may be exercised which requires to form other wiring layer on thesemiconductor substrate so that the plug layer mentioned above isconnected to said other wiring layer.

As clearly described above, using the manufacturing method according tothe present invention, it is possible to form a fine resist pattern at astep which uses a stopper film of silicon nitride. As a result, it ispossible to precisely form a highly-integrated multi-layerinterconnection structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1G show the manufacturing steps for the multi-layerinterconnection structure according to the present invention.

FIG. 2 is a graph showing a relationship between a thickness of and areflectance of an SiN film.

FIGS. 3A-3D show the manufacturing steps for a conventional multi-layerinterconnection structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A-1G show steps to manufacture a multi-layer interconnectionstructure generally denoted as 100 according to a preferred embodimentof the present invention. Among manufacturing steps, first, as shown inFIG. 1A, an inter-layer insulation layer 2 of SiO2 or the like with afilm thickness of about 2000 Å is formed on a semiconductor substrate 1of silicon or the like. Following this, a stopper film 3 of SiN isformed. The thickness of the stopper film 3 is selected from the rangeof about 1200 Å to about 1340 Å or the range of about 1730 Å to about1880 Å. More preferable thickness is about 1270 Å or about 1800 Å.

FIG. 2 is a graph showing a relationship between a film thickness and areflectance of an SiN film. The graph was obtained by measuring areflectance of an excimer laser (intensity of reflection light/intensityof incident light) in the condition that the excimer with a wavelengthof about 248 nm was impinged upon an SiN film formed on an SiO₂ layer.

As the graph clearly shows, when the thickness of the SiN film ispredetermined, it is possible to reduce the reflectance of the excimerlaser.

Next, as shown in FIG. 1B, a photoresist layer (not shown) is formed onthe stopper film 3. And the photoresist layer is exposed using anexcimer laser with a wavelength of about 248 nm, and a resist mask 4 isaccordingly formed.

At the exposure step, since the thickness of the stopper film 3 underthe photoresist layer is a predetermined film thickness as describedabove, it is possible to suppress a reflectance of the exposure light to0.3 or lower, and more preferably, 0.2 or lower. As a result, the resistmask 4 with a fine opening pattern is formed highly accurately andprecisely. It is possible to particularly avoid creation of a dimpleformed when interference between the incident light and the reflectionlight partially exposes the photoresist layer.

Next, as shown in FIG. 1C, after the stopper film 3 is patterned usingthe resist mask 4, the resist mask 4 is removed.

Then, as shown in FIG. 1D, the inter-layer insulation layer 2 is etchedusing the stopper film 3 as a mask, thereby forming an aperture portion5. The surface of the semiconductor substrate 1 is exposed in the bottomsurface of the aperture portion 5.

In this preferred embodiment, since the inter-layer insulation layer 2is etched using the stopper film 3 as a mask, the mask barely recedes,and the aperture portion 5 with a high aspect ratio is formed precisely.Alternatively, both the stopper film 3 and the inter-layer insulationlayer 2 may be etched using the resist mask 4 as customarily practiced.

Next, as shown in FIG. 1E, a conductive layer (not shown) of tungsten,for example, is formed in the aperture portion 5 and on the stopper film3 so as to fill up the aperture portion 5. Following this, theconductive layer is etched back from the top surface using the stopperfilm 3 as an etching stopper. This leaves the conductive layer onlyinside the aperture portion 5, and the conductive layer becomes a pluglayer 6. The conductive layer is etched back somewhat excessively sothat the conductive layer will not remain on the stopper film 3.Therefore, the top end of the plug layer 6 is slightly lower than thesurface of the stopper film 3.

Then, as shown in FIG. 1F, the stopper film 3 is removed by etching. Inconsequence, the top end of the plug layer 6 protrudes above the surfaceof the inter-layer insulation layer 2.

At last, as shown in FIG. 1G, a wiring layer 7 of copper, aluminum orthe like is formed on the inter-layer insulation layer 2 and the pluglayer 6. In this preferred embodiment, since the top end of the pluglayer 6 protrudes above the surface of the inter-layer insulation layer2, when the wiring layer 7 is formed, the wiring layer 7 and the pluglayer 6 are connected sufficiently with each other.

Through these steps, the multi-layer interconnection structure generallydenoted as 100 is completed.

Although the plug layer 6 does not completely fill up the apertureportion 5 but leaves a hollow portion as shown in FIG. 1G, since theaspect ratio of the aperture portion 5 is large in the multi-layerinterconnection structure 100, it is needless to mention that theaperture portion 5 may be completely filled up with the plug layer 6.

Further, while the multi-layer interconnection structure 100 is astructure in which the plug layer 6 connects the semiconductor substrate1 with the wiring layer 7, the multi-layer interconnection structure 100may be a structure as that shown in FIG. 3D, for instance, in which theplug layer 6 connects the wiring layer 7 with other wiring layer whichis formed on the semiconductor substrate 1.

What is claimed is:
 1. A method of manufacturing a semiconductor devicewith a multi-layer interconnection structure, comprising: a step toprepare a semiconductor substrate; a step to form an inter-layerinsulating layer on said semiconductor substrate; a silicon nitride filmforming step to form a silicon nitride film on said inter-layerinsulation layer; a step to form a photoresist layer on said siliconnitride film and to expose said photoresist with an excimer laser tothereby form a resist mask; an etching step to etch at least saidsilicon nitride film using said resist mask as an etching mask tothereby form an aperture portion; a step to deposit a conductive layerwithin said aperture portion and on said silicon nitride film; a step toetch back said conductive layer on said silicon nitride film using saidsilicon nitride film as a stopper so that said conductive layerremaining within said aperture portion becomes a plug layer; a step toremove said silicon nitride film so that a top end of said plug layerprotrudes above the surface of said inter-layer insulation layer; and astep to form a wiring layer connected with said plug layer on saidinter-layer insulation layer, wherein said silicon nitride film formingstep is a step to select a thickness of said silicon nitride film fromthe range of about 1200Å to about 1340Å and the range of about 1730Å toabout 1880Å to thereby reduce the reflectance of the reflection light ofsaid excimer laser which impinges upon said photoresist layer from theback surface of said photoresist layer relative to incident light 0.3 orsmaller.
 2. The method according to claim 1, wherein said siliconnitride film forming step is a step to select the film thickness of saidsilicon nitride film from the range of about 1230 Å to about 1310 Å andthe range of about 1760 Å to about 1850 Å.
 3. The method according toclaim 1, wherein said silicon nitride film forming step is a step toselect either about 1270 Å or about 1800 Å for the film thickness ofsaid silicon nitride film.
 4. The method of claim 1, wherein awavelength of said excimer laser is about 248 nm.
 5. The methodaccording to claim 1, wherein said etching step comprises a step to etchsaid silicon nitride film using said resist mask, and further a step toetch said inter-layer insulation layer after removing said resist mask,using said silicon nitride film as a mask.
 6. The method according toclaim 1, further comprising a step to form other wiring layer on saidsemiconductor substrate so that said plug layer is connected to saidother wiring layer.